Insights into the Relationship between Wettability and Surface Roughness in Tight Reservoirs from a Pore-Scale View: Effect of Electric Field

Abstract

The surface roughness of reservoirs detected by AFM is typically employed to predict the wettability of a sandstone reservoir. However, the resulting predictive relationship represents the surface roughness in only the intragranular region due to the limitations of the AFM probe. For a long time, the detection of surface roughness in the intergranular region, especially that of a sandstone reservoir treated with an external stimulus, has not attracted much attention. This paper proposed an in situ AFM and SEM method for measuring the surface roughness in the different regions of tight sandstone treated with an electric field, further revealing the wettability alteration from a pore-scale perspective. The results show that the electric field exposure increases the surface roughness in the intragranular and intergranular regions, synthetically strengthening the water-wetness of tight sandstone. Notably, pore parameter changes in the intragranular region differ from those in the intergranular region. Pore length decreases in the intragranular region and also in the intergranular region, and pore number remains unchanged in the intragranular region but decreases in the intergranular region. Moreover, pore depth increases in the intragranular region but decreases in the intergranular region. The movement of clay minerals induced by the electric field accounts for the difference in the roughness alteration in the two regions. This paper sheds light on new ways to approach surface roughness measurement that can greatly improve the understanding of the relationship between surface roughness and wettability of reservoirs. In addition, the work presented in this paper may be vital in determining the surface roughness of homogeneous materials treated by external stimulation.